Image detecting systems typically scan scene based images onto a focal plane array made up of individual detector elements. Each detector element within the focal plane array has a unique output voltage offset and gain reported upon detection of an image. The unique output voltage offsets and gains of the individual detector elements are a result of an inherent inability to produce identical detector elements during the manufacturing process. The inability to produce identical detector elements requires that an imaging system perform calibration on the focal plane array to compensate for the varying output voltage offsets and gains from one of the individual detector elements to another despite detecting identical portions of an image.
Calibration of imaging systems typically requires that calibration reference levels be viewed by the focal plane array during system operation. The calibration time can take time away from viewing the actual scene images. The calibration references of typical scan systems are produced by thermo-electrical devices that are optically viewed during the calibration period. Replacing the thermo-electrical devices with modified optical elements already in the system is desirable to reduce system complexity. Viewing these modified optical elements during normal scan return times also simplifies system operation.
Therefore, it is desirable to perform calibration with modified scene elements inherent within a typical scan system. From the foregoing, it may be appreciated that a need has arisen for scene based calibration of an image detecting system. In accordance with the present invention, a passive scene based calibration system is provided that substantially eliminates or reduces disadvantages and problems associated with conventional image detecting system calibration techniques.